Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method involving formation of a polymer emulsion by heating a monomer and undertaking a batch or semi-continuous emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in entirety. Other examples of emulsion/aggregation processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488, 5,977,210 and 5,994,020; and U.S. Pub. No. 2008/0107989, the disclosure of each of which hereby is incorporated by reference in entirety.
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins as illustrated, for example, in U.S. Pub. No. 2008/0153027, the disclosure of which is hereby incorporated by reference in entirety. Incorporation of those polyesters into toner requires formulation into emulsions prepared by solvent containing batch processes, for example, solvent flash emulsification and/or solvent-based phase inversion emulsification (PIE), both of which are time and energy-consuming.
Solvent-less latex emulsions have been formed in either a batch or extrusion process through the addition of a neutralizing solution, a surfactant solution and water to a thermally softened resin as illustrated, for example, in U.S. Pub. Nos. 2009/0208864 and 2009/0246680, the disclosure of each of which hereby is incorporated by reference in entirety. However, certain amorphous resins may be difficult to process without solvent because the resin does not have a sharp melting point and exhibits substantial viscosity, which may work against the formation of emulsions. In addition, certain amorphous resins are more susceptible to molecular weight degradation in a solvent-free process.
Typically polyester resin emulsions (latexes) for EA Ultra Low Melt (ULM) toners are obtained batch-wise in a stirred reaction vessel using PIE. Amorphous polyester resin is dissolved in a combination of two organic solvents, such as, methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) at elevated temperature to produce a homogenous organic mixture. A fixed amount of base solution (such as, ammonium hydroxide) is then added to neutralize acid end groups on the polyester chain followed by addition of de-ionized water (DIW) to form a uniform dispersion of polyester particle in water through phase inversion. Total process time generally exceeds 5 hours (including the ramp-up time).
Thus, there is a need for a shorter process cycle.